The present invention relates to a gas turbine engine, and more particularly to accessory gearboxes thereof.
Gas turbine engines often include a mechanically driven accessory gearbox to drive accessory systems such as, but not limited to, power generators, fuel pumps, oil pumps and hydraulic pumps. The power requirements for both military and commercial aircraft continue to increase demands on the accessory gearbox as the number of electrical systems within the aircraft continue to increase.
Conventional gas turbine engine accessory gearboxes use a gearbox housing mountable to an engine case section. Air pressurized labyrinth seals are typically used to maintain pressure within the accessory gearbox housing and prevent oil from leaking out around each accessory shaft, which drives each accessory system. Bleed air from the engine is communicated as seal air to the accessory shaft labyrinth seals by pipe cores incorporated within the gearbox housing.
The bleed air is typically sourced from sections of the engine to assure the seal air is below a predefined temperature (approximately 350° F.; 177° C.) so as to avoid effects on the typically aluminum gearbox housing and labyrinth seals. Oftentimes, such bleed air usage reduces engine efficiency or may not be available at such temperatures. As the seal core routings are often located in high stress areas, structural adjustments to accommodate the relatively high temperature bleed air may be required which may result in gearbox housing of increased weight.